Table of Content  Branch Up  

Small Cards: a challenge

08/26/2009

The challenge that using small prototyping cards represents is becoming more and more apparent.

For one part, register circuits have grown during the last week. Recently, the L-BUS was introduced and now I'm wondering how I'm going to raise flags and even detect fault conditions from the registers themselves. That will be by adding more chips, obviously. Will them fit?

In the other hand is the connector pin-count issue. I have designated 70 of the 96 pin available at Data Slots so only 26 are left for point-to-point control signals. My "standard signals" add 6 per register so the pin-count by itself limits my cards to have 4 registers at the most with only 2 pins left for additional signals.

That still matches my original plan (PC, SP, OR in one card; B, C, D, E in another card and A in the ALU card) but feeling as being pushed to the limits is not nice.

As per Control Slots (120 pins), 37 pins are designated already, 83 are available. A comprehensive count of register's control signals resulted in 55 total so there are still 28 pins available.

Not all of these remaining 28 pins can be connected in a bus (as the others are) because I will need a few of them (about 8) for point-to-point connections. For instance, the "End Of Interrupt" (EOI) signal coming from the Interrupt Controller.

I wouldn't like to make more significant changes to the design so for now I will keep going on with this tight situation.